Plot

Set in the early 1960s and during the era of Vatican II, a young woman in training to become a nun struggles with issues of faith, the changing church and sexuality.

1964. Cathleen Harris, in her late teens, has resided at the Convent of the Beloved Rose in her home state in the American south for close to two years, first as a postulant for six months, before taking her first vows to become a novice. Unlike the other postulants and novices, Sister Cathleen was raised in a household without religion, let alone Catholicism. As such, her decision to become a nun, which went against her divorced mother's wishes, may be more secure in her mind than her colleagues for which this life course may be more bred within them. The convent is led by the Mother Abbess, Reverend Mother Marie Saint Clare, whose entire life is this convent off of where she not stepped foot in forty years. Reverend Mother believes she is the voice of God within the walls of the convent, and thus does not tolerate any of the sisters questioning her authority. She also believes that the Catholicism which she has known all her life is perfect. When she receives an edict regarding the Second Vatican Council - more commonly referred to as Vatican II - which, opened in 1962 as a process to make the Catholic church more open to modern ideals, she refuses to implement any of the changes, let alone discuss the edict with any of the sisters, especially with the likes of Sister Mary Grace, the Mistress of Postulants and Novices who has more contemporary views of the church. Sister Cathleen's drive to become a nun is set against this backdrop, her process which is not as easy as it appears to the others, and whether she makes it to nun is affected by the Reverend Mother's strict methods and refusal to modernize.—Huggo

In 1954, seven-year-old Cathleen Harris lives in rural in Tennessee with her mother, Nora, a factory worker, who is non-religious but wants to show Cathleen a church and let her make her own decision. Cathleen's father, Chuck, comes home late, drunk, and argues with his wife. Chuck eventually leaves. Nora supports herself and picks up a series of men for one-night stands. At age 12, Cathleen seeks love of her own, and finds it in Catholicism when two nuns visit her home and offer her enrollment at a Catholic girls' school. The school offers her free tuition and a full scholarship to any college Cathleen chooses if her grades are excellent. At the school one day, a young nun befriends Cathleen and describes how she is married to Christ. At age 17 in the year 1964, after Cathleen comes home from school and runs into another one of her mother's pickups, Cathleen decides to leave home and give her life to God..

Raised by a vehemently non-religious, single mother (Nicholson) in rural Tennessee during the '50s, a scholarship to Catholic school soon finds Cathleen (Qualley) drawn into all the mystery and romanticism of a life devoted to the worship and servitude of God. With the dawn of the Vatican II era, radical changes in the Church are threatening the course of nuns' lives. Cathleen finds herself struggling with issues of faith, sexuality, and the changing administration.

This is a story of the effect of Vatican II (1962-65) on the Catholic Church, as seen in one convent, through the eyes of the tough old-fashioned Mother Superior, the kinder, younger, and more modern nuns, and the Postulants and Novices, particularly Sister Cathleen.

In 1954, seven-year-old Cathleen Harris (Eliza Manson) lives in rural in Tennessee with her mother, Nora (Julianne Nicholson), a factory worker, who is non-religious but wants to show Cathleen a church and let her make her own decision. Cathleen's father, Chuck (Chris Zylka), comes home late, drunk, and argues with his wife. Chuck eventually leaves. Nora supports herself and picks up a series of men for one-night stands.

At age 12, Cathleen (Sasha Mason) seeks love of her own, and finds it in Catholicism when two nuns visit her home and offer her enrollment at a Catholic girls' school. The school offers her free tuition and a full scholarship to any college Cathleen chooses if her grades are excellent. At the school one day, a young nun befriends Cathleen and describes how she is married to Christ. At age 17 in the year 1964, after Cathleen (Margaret Qualley) comes home from school and runs into another one of her mother's pickups, Cathleen decides to leave home and give her life to God.

With twenty other girls, Cathleen joins the Sisters of the Beloved Rose. She will be a postulate for six months in their convent, after which she will become a novice for a year and a half, and then make her final vows to become a nun. The Abbess, Reverend Mother Marie Saint-Clair (Melissa Leo), is tough, cold, traditional and largely responsible for training and disciplining the postulates. She leads the postulates through the weekly "chapter of faults," in which they must publicly confess to all their faults and face the accusation of the other postulates, for which Mother Superior assigns extreme, humiliating penances, including "The Discipline," a knotted whip that they use to flagellate themselves.

Sister Mary Grace (Dianna Agron), a young, warm, kind, and progressive nun, is the Postulant Mistress, who tries to make life easier for them. Most of the day is heavily regimented, but sometimes the postulates fall into girlish activities and giggling. Cathleen tends to avoid interacting with the other girls and spends her free time alone and reading from the Bible.

Mother Superior keeps getting envelopes from Archbishop McCarthy (Denis O'Hare) about Vatican II, which she ignores. Sister Mary Grace sees the documents, and says that change would be good. Mother Superior cuts her off with, "The Church is perfect exactly the way it is." Later, they argue, and Sister Mary Grace challenges Mother Superior's authority. Sister Mary Grace goes off to pray, and decides to leave the convent.

After six months, Cathleen takes her Simple Vows and becomes a novice. As Reverend Mother grows increasingly harsh, 18-year-old Sister Cathleen undergoes a sexual awakening. Cathleen stirs one night after masturbating in her sleep. She stops eating and interacting with the other novices and nuns over her "impure thoughts". When her mother visits the convent to deliver news about her father Chuck's passing, she notices Cathleen's pale and emaciated appearance. Nora threatens the Reverend Mother over her daughter's treatment, but Reverend Mother bushes it off, saying that Nora no longer has a daughter but that Cathleen has now given her life to the Church.

Cathleen eventually collapses during dinner one evening from starvation and dehydration, she is sent to the infirmary for several days where she confides in another young nun, Sister Emanuel (Rebecca Dayan). Later on, Cathleen sneaks out of the infirmary and into Sister Emanuel's room where Cathleen tells her that she longs for "comfort," leading to a kiss and their having lesbian sexual intercourse. After this, Cathleen leaves the infirmary and shows signs of recovery, is eating again and showing quiet happiness, but neither she or Sister Emanuel ever discuss their sexual encounter.

Meanwhile, Archbishop McCarthy pays a visit to the convent. He tells Mother Superior that "this order in particular" is having difficulty embracing the changes of Vatican II. She dismisses the "ridiculous reforms." He tells her that if she can't adapt to the changes, she will be replaced. As for "that old medieval stuff," the extreme penances, "That's gotta stop." Mother Superior is devastated. She fears God has abandoned her.

At a subsequent Chapter of Faults, a novice confesses that she questions God's existence. Mother Superior tells her she's tired of hearing of her spiritual wretchedness and assigns her no penance at all. When Cathleen goes next and confesses feeling the need to be emotionally comforted and about her one-time sexual encounter with another nun. Cathleen refuses to give away the nun's name and only asks for penance. Mother Superior forces Cathleen to crawl on her hands and knees and to beg for penance from each of the other novices, which finally brings Cathleen to tears. Mother Superior grants penance to Cathleen anyway. Afterwards, Sister Emanuel leaves the convent without saying goodbye to Cathleen.

Eventually, Mother Superior calls the congregation and reads aloud the Archbishop's memo about Vatican II. Priests will say the Mass in English, and face the congregation. Catholics must embrace religious tolerance. Nuns are no longer required to wear habits and can wear whatever they wish as their status is now reduced and equal to any lay Catholic.

Of the original twenty postulates, only five are left to profess their final vows to become solemnly professed nuns, among them is Cathleen. At their mass of Solemn Profession, the priest asks each of the novices, "What do you seek?" One answers that she wants to take her vows and marry Jesus Christ. The priest then asks Cathleen the same question. She answers, "I seek something more."